1. Field of the Invention
The present invention relates to the cutting of segmented-end timber webs of the type used in manufacture of roof trusses by the “Turb-O-Web”™ method. In particular, the invention relates to a segmented end shape for the ends of a roof truss web with three or more straight facets to approximate a semi-circular or other part circular end.
2. Description of Related Art
The Turb-O-Web method of roof truss construction—which is the subject of U.S. Pat. Nos. 6,176,060, 6,249,972, 6,415,511 and 6,688,067—offers substantial efficiency gains in the construction of oblique roof trusses for building construction, by adapting the truss construction to use webs having standardised tapered end shapes and, usually, also predetermined incremental lengths. The contents of those patents are incorporated herein by reference.
The preferred end shapes for the Turb-O-Web method are semicircular, but it is possible to use webs having a segmented end shape which approximates a semicircle by a series of 3 or more, preferably at least 5, straight facets at successive angles (usually 5 facets for 70 mm wide webs or 7 facets for 90 mm wide webs). True semicircular ends give the greatest accuracy, but these require specialised cutting machines. Segmented ends consisting of regular (ie. equal angle) half polygons seeking to simulate a semicircular web end may cause an accumulation of small errors over a succession of webs, causing the web-to-chord joint locations to vary somewhat from the locations predicted by the design software which calculates on the basis of semicircular ends. Greater accuracy can be achieved by increasing the number of facets but this requires saws having more blades than is provided for on the most common types of saws.